Table 3.
Relative risk of preterm birth and per cent of preterm births attributable to 2-day mean apparent temperature (AT) on a 24.9°C day versus an 18.6°C day, Detroit, Michigan area, May to September, 1991 to 2001
| Model | Knots in day-of-year spline | Covariates | Relative risk (95% CI) | Per cent attributable (95% CI) |
| 1 | 2 | None | 1.11 (1.02 to 1.09) | 9.9 (2.4 to 16.4) |
| 2 | 5 | None | 1.11 (1.03 to 1.20) | 9.8 (2.6 to 16.5) |
| 3 | 8 | None | 1.09 (1.01 to 1.18) | 8.1 (1.0 to 17.6) |
| 4 | 5 | Solar radiation, wind speed, precipitation | 1.12 (1.04 to 1.21) | 10.6 (3.8 to 17.2) |
| 5 | 5 | Solar radiation, wind speed, precipitation, inverse-odds weights* | 1.12 (1.02 to 1.21) | 10.4 (2.2 to 17.5) |
*Inverse-odds weights calculated from the predicted odds of AT given lag day 0 and 1 of ozone, PM10 and NO2.
NO2, nitrogen dioxide; PM10, 10 micrometres.